In wireless telecommunication, harmonics form on multiples of the base frequency. Harmonics are multiples of the base frequency and caused by the non-linear properties of the transmitter. If a harmonic is in the pass band of a nearby receiver and is sufficiently strong, the harmonic may weaken the performance of the receiver. If a sufficiently strong interfering signal not on the actual pass band of the receiver is directed to the receiver, the operation of the receiver may still be disturbed because of its non-linearity. As the number of wireless users increases and, on the other hand, as new transmission technologies are developed, many new frequency ranges are taken into use. Multiples of other frequency bands avoidably coincide with the frequency bands, i.e. harmonics may cause problems in the operation of the receivers. Multiples coincide particularly with non-licensed frequencies of over 5 GHz. Multiples of for instance DCS1800 (1710-1785 MHz), PCS1900 (1850-1910 MHz) and GSM900 (880-915 MHz) coincide with the 5-GHz band, for which different wireless local area network techniques have been developed. The IEEE 802.11a standard specifies one technology operating in this frequency range.
The problem caused by harmonics is emphasized when multimode terminals are developed that include a transceiver whose transmitter causes harmonics in the frequency range of another receiver or transceiver. Since the transmitter of the first transceiver and the receiver of the second transceiver are physically close, harmonics may cause strong interference in the operation of the receiver of the second transceiver.
A solution has been developed for terminals comprising a transceiver according to the GSM 850 technique (in the transmission frequency range 824 to 849 MHz) and a Bluetooth transceiver operating in a 2.4-GHz non-licensed frequency range, wherein the Bluetooth module uses radio measurements to specify radio transmissions in its environment, such as frequencies used by a GSM transmitter comprised by a terminal. The measurements are used to modify the hop set used in the Bluetooth module so as to avoid frequency ranges causing interference. This allows also the avoidance of sufficiently strong harmonics in the GSM transmitter. The drawback of this solution is the need for radio measurements and related equipment for avoiding harmonics. Many radio techniques also exist that do not use frequency hopping and, consequently, wherein frequency hopping settings cannot be changed to avoid harmonics.